Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.39   11.341%   $268.766   $268.77   $268.75   $268.80  
  Purchase #2 $91.95   5.675%   $97.1682   $97.17   $97.15   $97.20  
  Purchase #3 $244.80   8.776%   $266.2836   $266.28   $266.30   $266.30  
  Purchase #4 $103.34   7.172%   $110.7515   $110.75   $110.75   $110.80  
  Purchase #5 $77.39   11.295%   $86.1312   $86.13   $86.15   $86.10  
  Purchase #6 $203.70   3.628%   $211.0902   $211.09   $211.10   $211.10  
  Purchase #7 $18.76   12.839%   $21.1686   $21.17   $21.15   $21.20  
  7 purchase totals = $981.33       $1,061.3593   $1,061.36   $1,061.35   $1,061.50